Publications of the Astronomical Society of the Pacific 100:1405-1422, September 1988

STELLAR PHOTOMETRY IN THE PHOENIX DWARF GALAXY*

SERGIO ORTOLANI Osservatorio Astronómico di Padova, Vicolo dellOsservatorio 5, 35100 Padova, Italy AND RAFFAELE G. GRATTON Osservatorio Astronómico di Roma, Via del Parco Mellini 84, 00136 Roma, Italy Received 14 May 1988

ABSTRACT CCD photometry in Β and V, obtained at the ESO 2.2-m telescope, for a field in the Phoenix dwarf galaxy, is presented. Our data indicate that the galaxy is dominated by an old metal-poor population, similar to that of the galactic globular clusters M 3 and M 92. The distance modulus is somewhat uncertain ((m — M)v = 23.5 ± 0.5), but there are indications that the Phoenix dwarf galaxy belongs to the Local Group. A small amount (~ 104 SKq) 0fstars 0fa young population {t ~ 107 yrs) is also present. We suggest the Phoenix dwarf galaxy is a dwarf spheroidal galaxy in which a second recent burst of star formation has occurred. Key words: galaxies: individual-photometry-galaxies: Local Group

I. Introduction population of galaxies belonging to the Local Group, it An object of low surface brightness, apparently com- would be interesting to have some more insight into the posed of stellar images, was discovered by Schuster and nature of the Phoenix dwarf galaxy. West (1976) from an inspection of a ß plate for the ESO During an observing run in October 1984, we acquired (ß) survey, in Phoenix (a(1950) = 1^9^0, δ(1950) = a series of CCD frames through (7, B, V, and Ha filters of 44042'; ( = 272°, b = 69°). More extensive observations various regions in the galaxy. While most of the resulting by Canterna and Flower (1977), including photographic frames were of rather poor quality, we were able to have a photometry using the Racine wedge at the CTIO 4-m couple of good deep Β and V frames of the western region telescope, suggested that the object is a dwarf galaxy, of the galaxy, including the association of blue stars de- probably irregular, since some of the brightest stars (con- scribed by Canterna and Flower. A preliminary report centrated in a region on the west side of the object) are about these observations was presented in Gratton, Or- blue. Canterna and Flower estimated a distance modulus tolani, and Richter (1986). In this paper we present of26.33 ± 0.16 mag, by matching the C-M diagram they panoramic photometry of about 700 stars down to V = 24 obtained for the brightest stars (V <21.2) with the C-M within this frame. diagram of the brightest stars in IC 1613 (Sandage 1971; Π. Observations Sandage and Katem 1976). However, this procedure is quite ambiguous since the galaxy might be considerably A field (Fig. 1) in the Phoenix dwarf galaxy was ob- closer to us. This eventuality is also supported by the served both in Β and V in October 1984 with a back-illu- apparent lack of Η II regions. Considering this possibility, minated RCA CCD (ESO No. 2) at the Cassegrain focus of Richter (1984) included the Phoenix dwarf galaxy in a the European Southern Observatory (ESO) 2.2-m tele- catalog of possible Local Group members. Morras and scope at La Silla. The field is centered approximately 1 arc Bajaja (1986) surveyed at a rather coarse resolution the min W of the galaxy center. Bright UBV equatorial stan- Η I emission from a region including the Phoenix dwarf dards from Landolt (1983) were also observed on the same galaxy. They concluded that most of the radiation is due to night for calibration purposes. the neighboring Magellanic Stream, and it is not related The journal of observations is in Table I where filters, to the galaxy. A component possibly related to the galaxy exposure times, date and time of observation, and seeing _1 measured on the frames themselves (FWHM) are given. was detected at V(lsr) = 128 km s . Unfortunately, the -1 optical velocity of the galaxy is unknown. Given the small The scale of the array is approximately 0'/36 pixel . The resulting field is thus about 2 arc min X 3 arc min on the *Based on observations made at the ESO La Silla Observatory. 320 X 512 pixels target.

1405 © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 1406 ORTOLANI AND GRATTON

Fig. 1-Reproduction of the CCD program field, taken with the ESO RCA/CCD camera at the ESO 2.2-m telescope. The size of the field is 120" EW X 180" NS (320 X 512 pixels). North is down and east is to the right.

The frames were reduced for readout bias, flat field, the Garching facilities of the European Southern Obser- and dark current using suitable exposures taken during vatory. The last version of DAOPHOT code (including the same nights, by means of conventional procedures the ALLSTAR routine) was used. The point-spread func- (Mould, Kristian, and Da Costa 1983). tion (PSF) for each frame was defined from the sum of several relatively uncrowded, brighter stars. The usual ΠΙ. Reduction iterative process was followed of subtracting the ALL- Analysis of our CCD frames was done with the STAR-fitted stars from the frame, identiiying additional DAOPHOT code (Stetson 1987) loaded within the ones to be added to the list, and rerunning the fitting MIDAS-system running on the VAX-8600 computer at routine. About 700 stars were detected and measured in

TABLE I TABLE II Journal of Observations Photometry

Frame Filter Date U.T. Exp. time Seei ng ( sec ) Star σ( V) B-V σ(Β)

U 18/10/198^ 03:06 3600 T'S 25 6 18/10/198^ 04:09 2700 1 187.0 4.7 21.875 0.020 0.987 0.045 ^6 V 18/10/1984 04:56 1800 ^6 2 135,6 4.7 23.648 0.073 0.854 0. 124 27 Ha 18/10/1984 05:30 2700 11¼ 3 56.5 5.4 23.552 0.067 1 .091 0. 148 4 238. 1 14.6 21.585 0.017 1 . 155 0.027 5 222. 1 21.6 21.740 0.019 1 .213 0.035 6 258.3 23.3 21.056 0.010 1 .323 0.027 both the colors. 7 17.6 24.0 23.855 0. 100 0.641 0. 127 Zero points of the photometry were derived by measur- 8 129.3 26.4 22.517 0.033 0.761 0.033 ing the magnitude of some uncrowded images in each 9 87.5 39. ^ 21.335 0.018 1 .043 0.024 10 58.8 ^5.1 23.7½ 0.099 0.587 frame by means of HP-IHAP aperture magnitudes (at the 0. 103 11 7^.9 50.8 22.418 0.035 0.935 0.0^6 ESO Garching center) using a 7'/3-square aperture. The 12 220.9 51.6 21.032 0.012 1 .389 0.029 transformation to the standard Johnson system was en- 13 22^.1 58.8 23.252 0.056 1.138 0.1^5 sured by analogous reduction of bright equatorial stan- 14 5.7 61.3 23.779 0.169 0.803 0.131 dards (Landolt 1983). The transformation equations from 15 115.6 65.2 23.896 0.126 0.383 0.097 IHAP to Johnson BV magnitudes are: 16 249.8 66.3 21.999 0.018 0.819 0.025 17 186.0 75.8 21.895 0.016 1 .070 0.0M V = tw + (24.687 ± 0.008) (1) 18 61.6 71 .8 24.725 0.52^ 1.873 0.768 19 222.^ 73.8 22.0^9 1.189 0.039 and 0.025 20 96.7 78.3 22.158 0.028 0.777 0.0^0 {Β-V) = 1.121 (b - v)mA? + (0.436 ± 0.024) . (2) 21 9.0 77.9 23.830 0.077 -0.0^5 0.056 22 23^.3 87.1 23.580 0.082 1 .016 0.209 Equation (1) is valid for a 10-sec V exposure, while equa- 23 113.7 86. 1 21.732 0.016 1 .199 0.023 tion (2) holds for a ratio of 2 between the exposure times in 24 152.2 86. ^ 21.202 0.018 1.264 0.025 b and v. 25 89.6 90.3 23.791 0.100 0.^41 0.093 The color equations (1) and (2) are briefly discussed in 26 177.5 93.2 22.898 0.0^7 0.635 0.070 Gratton and Ortolani (1987) where observations of the 27 291.8 9^.0 23.926 0.143 0.085 0.089 cluster LMC:C0 435-589 in Reticulum, made during the 28 20.3 94.1 23.638 0.111 0.659 0.092 29 99.9 9^.^+ 22.811 0.0^8 0.871 0.070 same observing nights as the present observations of the 30 273.7 9^.4 22.846 0.067 0.82^ 0.085 Phoenix galaxy, are presented. We think that the magni- 31 163.6 96.5 23.773 0.065 0.723 0.128 tude scales of the present paper have errors not larger 32 111.9 99.3 22.513 0.03V 0.699 0.050 than 0.05 mag both in V and (Β — V) in the range 18 < V 33 57.8 101 .8 2^.080 o. m -0.111 0.115 <24. 34 219.2 102.3 20.762 o.oio 1.223 0.017 The complete list of reduced data is given in Table II. 35 151.0 105.9 22.281 0.026 1 .052 0.039 We have included only stars with data in both colors. We 36 75.0 107.6 23.605 0.066 0.066 0.070 do not produce magnitudes for stars brighter than V = 18 37 275.8 109.3 22.722 0.037 1 .090 0.072 110.4 22.240 0.023 (which are saturated in the V frame and, moreoever, do 38 251.6 0.032 -0.126 39 233.1 112.9 22.675 0.050 1 .017 0.070 not belong to the galaxy, being field stars as inferred from W 52.9 112.9 23.178 0.065 -0.236 0.046 low-dispersion spectra) and fainter than V = 24 (which are 41 134.1 114.8 21.559 0.020 0.958 0.020 affected by large observational errors). We also rejected 42 229.0 1 18.7 20.686 0.012 1 .009 0.014 from the list stars having values of the parameter χ (mea- 43 248.9 122.0 23.667 0. 125 0.838 0. 151 suring the goodness of the fits performed by the ALL- 44 239.3 125.3 23.125 0.049 0.478 0.042 STAR routine) larger than 1. The final list includes 622 45 107.9 125.4 23.655 0. 102 0.909 0. 156 stars. In Table II, the first column gives the star identifica- 46 120.2 126.0 23.088 0.071 0.822 0.069 0.815 0.083 tion number; the second and third columns give the χ and 47 285.0 130.6 23.229 0.076 48 272.2 131 .5 22.897 0.041 1.016 0.111 y coordinates on the V frame, in pixel units (1 pixel = 49 166.6 135.4 21.220 0.012 1 .257 0.028 0.363 arc sec; χ and y are measured from the northwestern 50 42.4 138.7 22.650 0.040 0.905 0.055 corner of the frame so that χ increases eastward and y 51 240.4 141.4 23.512 0.088 0. 138 0 . 079 increases southward); the fourth and sixth columns give 52 92.2 143.2 23.482 0.069 0.717 0.073 the reduced photometry; and, finally, the fifth and sev-

TABLE II (Continued) TABLE II (Continued)

Star Χ Ϋ V σ( V ) B-V σ(Β) Star Χ Ϋ ν ^77) σΠΤ

53 156.1 1^3.6 23.62^ 0.110 0.106 0.096 105 128.9 229.9 22.988 0.084 -0.158 0.046 5^ 50.7 1^7.1 22.927 0.064 0.674 0.077 106 69.5 230.4 24.149 0.102 1.500 0.414 55 21^.7 1^7.3 21.775 0.027 1.023 0.031 107 81.2 230.9 21.792 0.021 0.944 0.027 56 25^.0 1^7.1 22.669 0.037 0.590 0.074 108 191.3 232.2 20.085 0.008 1.125 0.009 57 181.6 1V7.7 22.737 0.049 0.731 0.053 109 66.0 236.3 24.058 0.118 0.285 0.126 58 127.5 150.1 21.3V7 0.021 1.283 0.027 110 33.5 234.8 20.769 0.011 1.470 0.021 59 177.2 152.9 23.629 0.123 0.383 0.095 111 184.0 235.7 21.505 0.015 0.038 0.012 60 21^.3 158.5 23.322 0.072 0.533 0.063 112 258.1 242.8 21.047 0.010 1.258 0.027 61 262.^ 162.^ 22.^60 0.043 0.238 0.037 113 12.2 248.1 23.651 0.110 0.170 0.070 62 159.8 163.3 23.217 0.078 0.876 0.090 114 173.0 254.4 22.134 0.036 0.127 0.039 63 166.3 163.5 21.32^ 0.015 1.395 0.023 115 154.7 259.9 23.302 0.100 0.399 0.077 6^ 182.5 166.5 22.632 0.042 0.732 0.042 116 83.1 260.1 21.828 0.020 1.033 0.038 65 153.9 170.1 2^.183 0.133 0.715 0.190 117 125.7 254.2 20.637 0.013 0.177 0.008 66 216.5 171.7 22.259 0.024 0.896 0.039 118 203.8 255.7 18.850 0.008 1.193 0.008 67 190.^ 172.2 21.M6 0.017 1.287 0.033 119 254.2 257.9 23.921 0.118 -0.071 0.069 68 71.6 172.6 23.^00 0.079 0.917 0.096 120 214.0 261.3 21.893 0.029 0.008 0.016 69 281.173.^ 22.650 0.052 0.442 0.046 121 246.9 264.9 21.912 0.027 1.004 0.038 70 292.^ m.9 21.^55 0.018 0.834 0.025 122 257.2 266.2 19.587 0.010 1.378 0.008 71 297.3 176.^ 22.592 0.046 0.915 0.071 123 222.7 266.7 22.909 0.046 0.192 0.039 72 118.7 180.4 23.221 0.053 0.689 0.063 124 117.0 267.5 21.867 0.026 1.036 0.032 73 41.0 182.4 23.750 0.117 0.557 0.121 125 107.4 269.8 23.204 0.047 0.891 0.094 74 179.0 187.4 23.174 0.073 0.813 0.099 126 306.8 271.7 21.772 0.021 -0.085 0.013 75 144.8 189.0 15.982 0.045 1.044 0.002 127 130.3 273.2 22.227 0.017 0.714 0.026 76 299.4 189.4 21.564 0.026 1.233 0.033 128 100.4 273.8 23.587 0.085 0.561 0.106 77 30.5 192.0 22.910 0.052 0.640 0.042 129 314.0 274.5 22.388 0.037 -0.101 0.023 78 125.9 191.9 24.767 0.551 -0.323 0.145 130 12.3 274.8 23.532 0.106 0.027 0.073 79 244.3 199.4 22.258 0.025 0.032 0.031 131 75.6 279.3 22.437 0.032 1.023 0.060 80 176.4 199.7 21.654 0.019 1.174 0.026 132 109.4 277.7 25.202 0.368 -0.060 0.250 81 53.5 199.5 23.707 0.081 0.675 0.114 133 149.6 276.7 22.784 0.045 0.811 0.067 82 265.0 201.8 22.545 0.040 0.898 0.052 134 91.6 279.7 22.494 0.041 0.871 0.038 83 132.7 206.9 22.808 0.049 0.185 0.044 135 238.9 279.7 22.343 0.038 -0.013 0.023 84 134.0 213.0 22.008 0.024 0.091 0.018 136 287.3 280.4 22.764 0.041 1.226 0.088 85 85.7 210.9 24.199 0.158 -0.195 0.120 137 160.1 283.1 21.763 0.031 0.101 0.024 86 237.9 211.6 22.350 0.060 -0.140 0.025 138 120.3 283.9 22.698 0.042 0.998 0.075 87 198.9 211.6 22.934 0.041 0.757 0.062 139 151.5 284.2 22.949 0.050 0.663 0.067 88 185.2 215.9 23.577 0.071 -0.180 0.056 140 200.3 284.4 20.314 0.008 0.733 0.009 89 160.1 217.7 22.259 0.019 1.116 0.048 141 136.3 284.7 23.503 0.074 1.182 0.154 90 229.4 223.0 21.764 0.025 0.755 0.030 142 43.0 287.5 21.616 0.015 1.240 0.028 91 32.8 219.4 23.524 0.083 0.507 0.066 143 265.8 289.6 22.487 0.046 0.624 0.044 92 261.4 220.5 24.300 0.179 0.672 0.223 144 260.2 290.0 21.890 0.023 0.687 0.025 93 282.8 222.4 24.296 0.218 -0.045 0.134 145 212.7 289.8 21.195 0.018 0.010 0.013 94 135.3 222.3 21.677 0.019 0.056 0.012 146 146.1 290.5 22.421 0.023 0.726 0.035 95 217.7 225.9 23.005 0.055 0.179 0.072 147 178.2 294.8 22.650 0.037 1.067 0.070 96 238.6 224.0 22.342 0.026 -0.036 0.028 148 137.9 296.0 21.849 0.016 -0.074 0.011 97 39.8 224.1 22.641 0.031 0.211 0.025 149 224.4 299.3 20.232 0.008 0.099 0.007 98 152.5 225.6 22.938 0.035 -0.129 0.039 150 202.2 305.8 19.122 0.006 1.710 0.006 99 313.1 225.3 23.696 0.091 -0.208 0.073 151 191.0 308.2 21.744 0.024 -0.051 0.014 100 202.4 225.8 20.002 0.007 1.137 0.009 152 170.1 314.2 22.746 0.088 -0.112 0.030 101 97.4 226.3 23.357 0.073 0.837 0.099 153 23.7 316.7 23.707 0.073 0.048 0.083 102 273.1 229.3 22.537 0.038 -0.162 0.019 154 143.2 320.9 22.685 0.049 0.548 0.034 103 177.4 229.7 22.750 0.070 0.020 0.029 155 300.8 323.5 22.925 0.052 1.053 0.103 104 264.8 229.4 20.813 0.011 1.513 0.015 156 189.4 323.0 22.263 0.026 1.442 0.052

TABLE II (Continued) TABLE II (Continued)

Star ( V) σ B-V σ( Β ) Star σ( V ) B-V σ(Β)

157 104.6 323.7 23.110 O.073 0.900 0.091 209 37.7 420.6 23.176 0.065 1.168 0.116 158 246.0 328.3 S3.887 0.147 0.413 0.117 210 310.9 421.8 23.900 0.101 0.646 0.197 159 297.3 332.5 20.764 0.013 1.575 0.026 211 241.2 421.2 20.582 0.008 1.306 0.013 160 227.2 331.3 20.879 0.011 1.604 0.021 212 224.6 424.6 23.019 0.058 0.900 0.083 161 100.7 333.4 21.117 0.010 1.324 0.023 213 135.1 426.0 21.376 0.015 1,112 0,018 162 153.3 334.4 23.383 0.060 -0.012 0.061 214 212.1 427.2 21.769 0.026 1.236 0.036 163 89.4 334.6 22.214 0.023 0.867 0.033 215 259.0 432.4 22.376 0.029 0.983 0.052 164 267.6 334.9 21.809 0.021 1.168 0.039 216 149.6 439.8 23.603 0.081 0.032 0.061 165 56.9 335:6 23.392 0.060 0.647 0.063 217 119.4 442.5 20.984 0.008 1.242 0,019 166 309.7 335.6 23.859 0.143 0.764 0.155 218 108,2 446.4 21,971 0,027 0.939 0.030 167 192.4 337.0 22.321 0.028 -0.104 0.019 219 76.0 447.2 23.728 0.183 0.715 0.118 168 223.3 339.9 23.762 0.141 0.637 0.144 220 139.3 449.4 23.096 0.078 0.995 0.065 169 308.4 342.2 21.514 0.016 1.084 0.033 221 59.0 464.9 25.590 0.681 0,899 1.033 170 12.3 342.8 23.905 0.123 -0.031 0.063 222 146.9 474.9 22.658 0.042 0.775 0.045 171 150.9 342.7 21.922 0.018 1.127 0.038 223 132.0 475.5 20.828 0.015 1.181 0.015 172 280.6 344.2 21.874 0.019 1.073 0.038 224 187.9 478.9 20.314 0.009 1.690 0.016 173 264.3 347.3 22.200 0.026 0.971 0.038 225 140.7 478.4 23.526 0.092 0.633 0.125 174 274.8 348.2 23.263 0.072 0.763 0.118 226 93.7 481.3 21.484 0.018 1.186 0.032 175 309.8 349.1 23.984 0.173 0.462 0.136 227 15.9 482.8 23.610 0.093 0.794 0.141 176 117.2 350.0 22.161 0.021 0.906 0.036 228 186.5 486.2 23.097 0.075 0.973 0.234 177 22.3 353.1 23.581 0.084 0.764 0.125 229 141.3 485.2 22.938 0.050 0.965 0.088 178 75.4 356.7 22.316 0.028 0.803 0.046 230 271.8 495.5 20.903 0.014 1.239 0.025 179 285.6 357.3 24.027 0.146 0.939 0.289 231 170.2 498.4 22.387 0.025 1.101 0.065 180 161.3 357.3 23.958 0.135 0.744 0.156 232 240.3 500.5 23.101 0.048 0.460 0.098 181 55.3 360.0 22.766 0.032 -0.055 0.029 233 70.8 504.4 22.223 0.030 0.847 0.033 182 225.9 362.0 23.335 0.068 0.325 0.072 234 158.6 507.6 23.460 0.089 0.452 0.081 183 172.6 363.7 23.266 0.071 1.173 0.109 235 87.6 509.7 23.126 0.069 0.485 0.070 184 143.3 373.1 22,228 0.028 1.069 0.064 236 191.4 12.7 23.706 0.116 0.491 0.124 185 94.0 368.4 21.363 0.012 1.085 0.018 237 263.2 14.2 22.473 0.106 0.608 0.048 186 198.6 368.5 21.431 0.014 1.308 0.035 238 268.5 23.6 23.456 0.114 0.246 0.063 187 258.3 374.0 24.871 0.306 -0.270 0.284 239 278.9 19.1 20.908 0.009 1.368 0.021 188 274.3 369.2 22.077 0.031 0.603 0.034 240 160.9 31.3 21.292 0.017 1.267 0.019 189 7.9 371.5 24.622 0.297 0.654 0.286 241 225.4 32.1 24.200 0.141 0.529 0.210 190 130.5 371.4 22.449 0.034 1.157 0.059 242 240.6 38.3 22.590 0.036 0.986 0.069 191 121.0 375.4 23.638 0.101 0.754 0.132 243 277.9 42.3 23.995 0.108 0.502 0.189 192 83.9 377.5 21.574 0.018 1.092 0.023 244 126.5 47.0 22.906 0.055 0.829 0.053 193 32.2 381.5 23.122 0.048 1.217 0.110 245 245.6 55.6 23.977 0.151 1.130 0.308 194 181.1 382.6 23.940 0.116 0.064 0.102 246 285.5 56.3 23.367 0.062 0.399 0.098 195 230.9 382.9 23.966 0.119 0.810 0.197 247 176.7 56.8 24.824 0.315 0.513 0.328 196 24.7 387.4 23.446 0.056 0.767 0.122 248 95.7 70.5 23.620 0.060 0.714 0.133 197 248.5 393.6 22.687 0.040 1.360 0.080 249 302.3 75.9 23.479 0.082 0.330 0.089 198 210.8 393.0 24.559 0.262 0.295 0.180 250 273.6 71.8 23.019 0.052 0.997 0.101 199 293.6 397.3 22.408 0.031 0,769 0.055 251 275.4 82.4 23.178 0.077 0.616 0.074 200 107.2 402.1 22.393 0.042 1.189 0.075 252 243.1 88.5 23.832 0.115 0.686 0.151 201 33.9 398.5 23.454 0.078 0.671 0.089 253 298.1 90.3 22.196 0.024 1.033 0.064 202 220,9 399.3 23.207 0.075 0.721 0.078 254 303.1 95.1 23.411 0,074 0.763 0.202 203 75.7 404.2 22.043 0.026 1.073 0.040 255 152.2 98.2 23.541 0.078 0.505 0.122 204 228.4 409.4 23.017 0.071 0.719 0.099 256 264.5 94.6 21.564 0.021 0.952 0.045 205 214.4 410.2 22.496 0.040 0.730 0.037 257 13.1 97.7 23.510 0.081 0.740 0.080 206 298.3 412.2 23.022 0.062 0.813 0.109 258 253.2 99.5 23.538 0.071 1.252 0.241 207 7.3 414.0 22.776 0.047 0.730 0.049 259 236.9 100.7 22.114 0.023 1.026 0.039 208 12.2 419.5 24.153 0.158 -0.096 0.103 260 66.7 103.8 20.843 0.012 1.492 0.016

TABLE II (Continued) TABLE II (Continued)

Star χ Y V

261 37.1 105.8 2^.699 0.260 1.078 0.440 262 187.7 107.2 21.776 0.022 1.117 0.030 313 192 .0 215 1 22 .698 0.034 -0.101 0.038 263 77.2 115.3 23.730 0.115 0.680 0.128 314 315 .1 218, 8 22 .471 0.049 0.804 0.057 26^ 218.2 121.1 23.^71 0.070 0.819 0.182 315 270 .6 222 4 20 .449 0.011 0.776 0.013 265 309.3 117.5 21.070 0.011 1.202 0.025 316 306 222. 23 . 138 0.051 0.209 0.060 317 250 .6 225 24 .008 0.177 -0.389 0.062 266 51.2 117.^ 21.^98 0.016 0.863 0.023 318 286 .5 226. 23. 267 259.6 119.1 23.88^ 0.101 1.436 0.249 .465 0.087 -0.393 0.059 319 221 . 1 231 22..870 0.055 0.184 0.040 268 91.8 118.8 23.529 0.081 0.465 0.095 320 241 .8 231. 23..312 269 199.2 127.2 22.665 0.042 0.798 0.061 0.073 0.235 0.070 321 258 .0 232 21..481 0.024 1.192 0.031 270 33.3 122.6 23.376 0.062 0.847 0.106 322 260 .8 236. 21..715 0.027 -0.145 0.012 271 170.^ 126.^ 22.922 0.038 0.905 0.088 323 214 .2 235 23..533 0.085 -0.014 0.073 272 311.5 128.2 20.978 0.014 1.398 0.027 324 202 .7 235. 21..510 0.026 0.060 0.020 273 ^9.1 130.4 25.131 0.405 1.384 0.671 325 85 .7 235, 8 22..380 0.029 1.205 0.059 0.023 1.125 0.038 274 133.3 131.9 21.914 326 237 237. 6 21..532 0.016 0.788 0.031 0.021 1.270 0.038 275 113.7 137.9 21.291 327 318 242 23..653 0.125 -0.308 0.056 0.230 -0.714 0.044 276 72.7 135.6 23.658 328 223 244. 21..619 0.027 -0.022 0.033 0.055 0.548 0.100 277 225.8 140.1 22.676 329 177 246 22..841 0.038 0.992 0.074 278 298.3 138.7 23.943 0.107 0.442 0.125 330 163 246. 23..775 0.113 0.626 0.141 279 239.1 145.9 22.988 0.066 0.564 0.061 331 123 247 ( 23..349 0.061 -0.216 0.060 280 206.9 150.1 21.822 0.023 0.931 0.032 332 213 248. 23..131 0.100 0.414 0.066 0.012 1.222 0.028 281 157.8 148.9 21.085 333 276 250, 23.. 151 0.075 -0.076 0.047 282 300.8 149.6 21.168 0.011 1.257 0.025 334 145 250. 22..511 0.044 0.718 0.043 283 193.9 153.9 21.990 0.035 0.942 0.047 335 75 255. 23..114 0.046 1.136 0.177 284 285.7 154.1 21.716 0.016 1.135 0.035 336 287 254. 22. 467 0.033 -0.193 0.027 285 264.1 154.6 23.301 0.065 0.883 0.097 337 277 257. 20. 537 0.010 0.782 0.011 286 139.8 160.1 24.110 0.135 0.749 0.198 338 242 1 260. 20. 706 0.011 0.903 0.022 287 89.0 163.2 23.546 0.092 0.454 0.073 339 168 3 260, 19. 895 0.008 0.082 0.009 288 94.9 165.2 23.620 0.104 0.134 0.068 340 266 261. 20. 767 0.011 0.046 0.008 289 240.7 165.7 21.083 0.010 1.323 0.027 341 136 262, 20. 092 0.009 0.846 0.009' 290 309.2 167.5 21.400 0.019 1.354 0.037 342 275 275 22. 265 0.027 1.330 0.064 291 168.0 173.5 23.534 0.078 0.183 0.077 343 190 279 21. 836 0.019 1.018 0.040 292 183.3 173.6 24.102 0.146 0.646 0.183 344 309 282 23. 687 0.120 0.287 0.134 293 65.0 177.1 23.334 0.074 0.557 0.099 345 305 285 22. 128 0.039 1.208 0.066 294 165.4 187.9 23.381 0.190 0.937 0.115 346 294 286 8 21. 812 0.022 1.078 0.034 295 171.0 190.4 23.207 0.093 1.080 0.121 347 14 288 4 23. 954 0.158 0.650 0.181 296 192.5 184.2 20.914 0.032 1.389 0.035 348 158 291 7 23. 314 0.080 0.611 0.072 297 249.0 185.0 22.218 0.028 -0.097 0.026 349 149 .0 302 6 23. 129 0.045 0.154 0.061 298 47.3 185.1 23.450 0.051 0.788 0.096 350 160 .7 302 6 23. 462 0.077 0.683 0.152 299 25.5 186.8 22.058 0.025 0.982 0.028 351 303 .3 301 8 22. 875 0.065 0.701 0.086 300 309.6 188.0 21.622 0.022 0.062 0.014 352 216 .9 302 O 22. 513 0.036 0.801 0.093 301 52.5 192.4 24.831 0.226 -0.159 0.173 353 214 .8 307 22. 836 0.044 0.544 0.052 302 5.8 196.5 23.265 0.068 0.959 0.095 354 25 304 22. 972 0.046 0.014 0.040 303 251.5 201.0 22.354 0.037 -0.353 0.029 355 90 307 24. 021 0.124 0.374 0.141 304 256.0 205.2 19.791 0.007 -0.022 0.006 356 122 309 22. 904 0.062 0.500 0.055 305 184.2 201.4 23.150 0.062 0.059 0.045 357 224 310 O 23. 315 0.078 0.157 0.048 306 204.2 202.0 22.832 0.038 0.742 0.046 358 62 320, O 23. 292 0.056 0.155 0.052 307 278.9 205.7 22.339 0.029 1.020 0.049 359 90 321 20. 946 0.010 1.480 0.021 308 151.4 208.3 23.315 0.397 0.927 0.142 360 171 8 322 21 . 835 0.017 1.418 0.039 309 248.5 216.0 22.162 0.029 -0.093 0.025 361 231 3 326 22. 747 0.057 0.934 0.068 310 244.1 219.4 21.093 0.013 1.372 0.033 362 272 2 328 21 . 801 0.021 1.200 0.034 311 266.7 215.3 22.110 0.022 0.803 0.038 363 287 1 331 22. 369 0.031 0.992 0.057 312 296.5 214.2 20.144 0.007 1.121 0.012 364 264 2 339 24. 000 0.209 0.177 0.140

TABLE II (Continued), TABLE II (Continued)

Star Y V a(V) B-V σ(Β) Star a(V) B-V σ(Β)

365 267.7 3^1.9 22.625 0.053 0.699 0.055 417 107.1 502.5 23.748 0.120 0.459 0.110 366 2^1.2 3^2.6 21.9Í»1 0.020 0.^26 0.030 418 96.3 505.6 23.845 0.105 0.991 0.173 367 233.8 3^5.3 23.850 0.103 0.^26 0.163 419 276.6 507.7 22.262 0.028 0.941 0.038 368 170.7 3^3.9 23.875 0.106 1.399 0.316 420 176.8 6.1 22.880 0.042 0.828 0.067 369 97.7 3^8.8 22.370 0.043 0.749 0.040 421 312.8 7.6 22.744 0.041 0.821 0.119 370 303.1 350.2 20.903 0.012 1.437 0.017 422 223.0 11.0 23.454 0.094 0.721 0.115 371 200.3 351.5 16.241 0.022 0.670 0.002 423 206.2 17.2 22.489 0.036 0.879 0.046 372 87.5 353.8 20.616 0.008 1.029 0.016 424 30.5 24.3 23.943 0.112 0.490 0.140 373 311.2 361.7 21.707 0.021 0.454 0.022 425 21.9 29.3 23.285 0.064 0.633 0.072 374 262.5 371.2 23.706 0.099 0.328 0.155 426 198.0 34.0 23.089 0.069 0.811 0.078 375 54.6 381.0 22.775 0.050 0.721 0.072 427 200.0 38.4 22.647 0.045 0.908 0.061 376 257.7 381.0 23.411 0.086 0.498 0.122 428 252.7 59.9 23.662 0.096 0.720 0..136 377 13.0 385.4 23.885 0.115 -0.015 0.082 429 152.7 51.8 22.037 0.029 0.960 0.058 378 212.1 386.0 21.255 0.014 1.088 0.023 430 19.2 54.8 23.924 0.123 0.880 0.170 379 230.9 394.4 24.117 0.146 1.395 0.290 431 234.2 60.7 21.962 0.027 1.302 0.091 380 301.7 401.3 23.222 0.080 0.775 0.071 432 178.2 64.0 23.613 0.102 1.108 0.205 381 242.6 407.5 22.542 0.028 1.513 0.083 433 293.6 66.2 23.566 0.081 0.787 0.142 382 93.1 408.0 24.142 0.130 0.761 0.177 434 308.9 71.8 21.907 0.020 1.051 0.044 383 287.3 410.9 23.154 0.062 0.557 0.075 435 253.1 76.2 23.008 0.051 0.985 0.091 384 60.4 417.9 23.466 0.068 0.263 0.058 436 164.7 78.8 23.054 0.050 0.431 0.057 385 300.7 421.2 23.435 0.072 1.079 0.177 437 204.0 80.0 21.647 0.018 0.805 0.028 386 276.1 428.2 23.374 0.098 0.571 0.078 438 137.0 79.8 23.846 0.118 0.889 0.152 387 67.8 431.4 23.980 0.168 0.167 0.098 439 238.8 83.1 23.189 0.072 0.798 0.091 388 293.2 435.0 23.963 0.134 1.000 0.209 440 315.3 89.7 23.428 0.078 0.883 0.126 389 318.1 440.9 22.859 0.038 1.000 0.082 441 183.2 99.2 22.775 0.040 1.080 0.062 390 126.7 440.5 23.275 0.082 0.582 0.079 442 234.1 100.7 23.815 0.085 0.671 0.152 391 81.1 441.8 22.833 0.043 0.976 0.055 443 317.7 100.4 23.067 0.072 0.999 0.104 392 234.8 442.1 22.292 0.030 1.052 0.069 444 73.2 120.3 23.607 0.081 0.806 0.108 393 215.1 445.3 22.548 0.044 0.507 0.047 445 57.0 133,1 23.382 0.070 0.997 0.144 394 275.6 453.2 22.163 0.030 0.625 0.042 446 109.5 134.2 22.484 0.045 0.814 0.049 395 302.5 447.3 22.855 0.051 0.715 0.076 447 83.8 134.6 22.495 0.030 1.635 0.118 396 87.3 453.7 23.166 0.055 0.803 0.107 448 270.3 138.2 22.140 0.023 0.663 0.048 397 136.2 458.3 23.779 0.115 0.209 0.101 449 146.4 149.2 23.393 0.087 0.941 0.147 398 194.9 463.6 23.418 0.092 1.064 0.142 450 104.3 151.7 23.168 0.057 0.768 0.077 399 7.1 464.2 23.893 0.122 -0.177 0.078 451 13.8 155.8 23.717 0.085 1.205 0.276 400 95.2 466.8 24.172 0.169 0.672 0.206 452 46.9 157.6 23.952 0.107 0.628 0.121 401 122.2 467.4 20.996 0.009 1.122 0.022 453 204.6 160.1 22.646 0.045 0.765 0.054 402 161.0 474.5 23.048 0.043 0.835 0.060 454 149.6 200.0 21.558 0.021 0.987 0.044 403 180.9 474.6 21.073 0.014 1.297 0.018 455 215.4 201.7 21.278 0.018 1.042 0.038 404 110.7 477.7 23.147 0.074 0.589 0.090 456 79.8 210.3 22.662 0.047 0.622 0.077 405 117.3 479.0 24.188 0.175 0.195 0.135 457 199.3 218.6 22.535 0.053 -0.071 0.041 406 25.3 479.5 23.692 0.084 0.455 0.071 458 226.4 219.1 21.881 0.025 0.854 0.030 407 65.4 484.7 23.998 0.131 1.126 0.246 459 177.6 219.1 24.424 0.177 -0.338 0.114 408 214.7 486.4 22.044 0.029 1.206 0.084 460 213.8 223.4 22.059 0.033 0.090 0.024 409 288.2 488.9 21.060 0.010 1.304 0.027 461 228.8 230.0 21.822 0.026 -0.325 0.026 410 143.1 492.9 22.320 0.034 1.009 0.089 462 117.9 232.3 21.998 0.023 1.039 0.045 411 124.8 494.5 22.203 0.091 0.786 0.060 463 307.1 236.4 22.182 0.032 0.692 0.039 412 122.4 495.8 22.046 0.085 0.884 0.055 464 150.7 243.4 21.752 0.038 0.488 0.044 413 217.8 497.9 22.362 0.039 0.867 0.046 465 143.4 242.7 21.194 0.022 0.502 0.035 414 50.0 498.3 23.708 0.103 0.880 0.138 466 114.7 247.4 21.185 0.015 1.082 0.027 415 11.0 498.4 23.107 0.081 0.458 0.051 467 297.8 251.3 23.292 0.087 0.118 0.053 416 162.4 499.1 22.620 0.050 0.889 0.050 468 163'.2 253.8 23.248 0.106 0.208 0.080

TABLE II (Continued) TABLE II (Continued)

Star Χ Y V σ(ν) Β -V σ(Β) Star X Y V σ(ν) Β V σ(Β)

^69 15Ε.9 352.8 O.m -0.017 0.096 521 229.6 139.1 22.966 0.03¿+ 0. 6¿+9 0.082 ¿♦70 221 .2 258.9 22. 1^1 0.021 -0.037 0.023 522 2¿U.0 156.7 20.929 0.016 1.316 0.0¿+0 ¿♦71 22¿t.8 277.6 22. l¿+8 0.029 0.897 0. 0¿+B 523 17.5 173.1 23.587 0.107 O. ¿+70 0.088 ¿♦72 18^.3 285.2 22.266 0.027 O. ¿^59 0. 0¿^2 52¿+ 221 . 1 189.2 22.659 0.033 0.890 0.051 ¿♦73 238.8 303.1 23.¿+70 0.095 0.683 0.118 525 270.6 192.3 23. l¿+5 0.055 0.668 0.069 ¿♦7¿^ 188.1 297.6 23.¿+52 0.083 0.272 0.079 526 206.1 193.5 23.931 0.119 0.436 0.117 ¿♦75 300.9 307.9 23.052 0.071 1.007 0.100 527 P79 . ^ 198.9 22.h0¿+ 0.033 0.805 0.060 ¿♦76 175.7 309.5 22.19¿^ 0.032 -0.003 0.025 528 251.8 211.9 22.652 0.050 -0.179 0.0¿+5 529 255.9 213.3 23.822 ¿♦77 2¿^¿» .8 313.¿^ 23.293 0.078 O. ¿^ 12 0.077 0.188 -0.780 0.083 ¿♦78 223.9 316.6 23.563 0.130 0.385 0.113 530 295.¿+ 238.3 2¿^.136 0.150 0.763 0.253 ¿♦79 256.6 328.1 2¿^.519 0.215 1 .¿^21 0.579 531 266.6 237.1 23.603 0.178 -0.328 0.060 ¿♦80 199.8 332.8 22.036 0.031 0.051 0.029 532 302.238.8 23.130 0.069 0.587 0.092 ¿♦81 129.¿^ 335.9 22.7¿^9 0.056 0.97¿^ 0.057 533 313.5 26¿+.9 23.700 0.129 0. 17¿+ 0.091 ¿♦82 217.2 336.1 22.55¿^ 0.036 0.810 0.06¿^ 53¿+ 199.3 27¿+.9 22.039 0. 0¿+2 0.553 0.035 ¿♦83 129.8 3¿^9.6 23.535 0.066 0. 9¿^5 0.139 535 25¿+.7 276.¿f 2¿^.007 0. 13¿+ 0.258 0.151 ¿♦8¿^ 269.8 355.7 21.689 0.01¿^ 1.315 0.0¿^7 536 2¿+2.8 296.6 23.391 0.08¿+ 0.680 0. 1 ¿+3 537 311.0 297.2 22.381 ¿♦85 8.9 358.6 23.¿^57 0.062 0.612 0.082 0.0¿+5 -0.073 0.0¿+3 ¿♦86 209.0 365.3 21.853 0.022 0.906 0.037 538 285.6 303.9 22.532 0. 0¿+3 1.136 0.107 ¿♦87 266.9 365.9 23.393 0.067 0.152 0.073 539 136.3 313.9 23.377 0.067 0.182 0.070 ¿♦88 255.7 368.7 2¿^.060 0.128 0.163 0.123 5¿♦O 232.9 311.1 22.75¿^ 0.0¿+l 1 . 0¿+7 0.059 ¿♦89 62.7 369.5 23.525 0.12¿^ 1.095 0.18¿^ 5¿+1 309.^ 319.3 23.138 0.083 1 . 0¿+3 0.136 ¿♦90 300.¿^ 372.¿^ 22.672 0.060 -0.078 0.0¿^2 5¿^2 313.1 321.2 22.669 0.05¿+ 1.083 0.082 ¿♦91 297.9 378.2 22.076 0.021 0.879 0.0¿^6 5¿+3 259.1 321.1 21.913 0.020 1.117 0.053 ¿♦92 309.1 372.9 18.511 0.007 1.533 0.007 5¿^¿+ 12¿^. 1 356.9 22.923 0.0¿+¿+ 0.917 0.073 ¿♦93 76.9 386.7 22.661 0.028 0.78¿^ 0.059 5¿t5 28¿+.2 373.8 22.518 0.0¿+0 0.786 0.05¿+ ¿♦9¿^ 96.2 388.0 23.^21 0.083 0.131 0.071 5^6 2¿^0.1 37¿+.3 22.8¿^1 0.059 -0.202 0.035 ¿♦95 198.9 388.1 23.¿^77 0.081 0.881 0.112 5¿+7 2¿+¿+.3 376.3 22.872 0.053 0.711 0.083 ¿♦96 15¿^.2 391.6 23.250 0.062 0.837 0.102 5¿^a 178.3 395.0 22.195 0.0¿+l 1.805 0.069 ¿♦97 300.0 39¿^.2 23.180 0.055 0.369 0.077 5¿i9 173.6 ¿+12.6 23.0¿+9 0. 0¿+6 1.237 0.106 ¿♦98 280.5 39¿^.3 23.182 0.07¿^ 0.708 0.170 550 307.2 ¿+28.5 22.016 0.033 1.066 0.035 ¿♦99 93.8 398.3 23.851 0.136 1.136 0.265 551 191.0 ¿+39.2 21.567 0.022 1.189 0.039 500 2¿^6.1 ¿^32.5 22.881 0.035 0.968 0.087 552 293.7 ¿♦¿♦S.S 22.000 0.023 0. 7¿+1 0.0¿+l 501 278.2 ¿♦3¿^.0 23.017 0.056 0.625 0.121 553 217.9 ¿+51.0 23.273 0.071 O. ¿+87 0.068 502 1¿^ 1.2 ¿♦3¿^.7 23.¿^55 0.088 0.357 0.099 55¿+ 118.1 2¿+.202 O . 15¿+ 0.192 0. 13¿+ 503 15¿^-3 ¿♦¿♦7.5 2¿^.622 0.218 -0.320 0.139 555 209.1 ¿+72. 1 22.835 0. 0¿+5 0.956 0.086 50¿^ 280.8 ¿ ¿ 9.0 22.976 0. 0¿^6 0.887 0.071 556 168.7 ¿+72.6 23.263 O . 08¿+ O . ¿+9¿+ 0.059 ♦ ♦ 557 237.1 ¿+73.7 23.213 505 10¿k0 ¿^61.3 23.196 0.065 0.217 0. 0¿^3 0.071 0.872 0.117 0.172 1 . ¿+62 0.279 506 201.¿+ ¿^87.2 23.9¿^8 0.116 0.615 0.196 558 2¿+6.3 ¿+85.3 23.8¿+3 559 306.7 ¿+93.5 22.596 507 261.6 3.0 21.338 0.01¿^ 1.365 0.030 0.03¿+ 0.89¿+ 0.060 508 216.1 3.8 23.559 0.062 0.611 0.171 560 66.5 ¿+98.2 2¿+.738 0. 2¿+7 1 . 8¿+7 1.226 509 21¿+.7 2¿^.9 22.58¿^ 0.037 0.837 0.061 561 172.¿+ 510.1 21.¿+21 0.03¿+ 1 . ¿+09 0.038 510 110.5 30.3 23.05¿^ 0.057 0.800 0.076 562 86.0 22.7 23.096 0.058 1.026 0.1¿+0 511 266.9 69.6 23.825 0.20¿^ 0.387 O. l¿+3 563 261.6 86.9 23.6¿+¿+ 0.112 -0.055 0.070 512 176.3 106.8 22.988 0.0¿^7 0.817 0.088 56¿+ 68.3 96.6 22.658 0.038 0.826 0.067 513 260.7 110.0 22.¿^72 0. 0¿^2 0.67¿^ 0. 0¿^7 565 1¿+1.1 111.5 23.292 0.057 1.180 0.121 51¿+ 182.3 119.3 22.778 0.053 0.831 0.07¿^ 566 112.7 153.9 23.719 0.109 0.676 0.1¿+¿+ 515 275.5 118.9 23.103 0.077 O. ¿♦6¿^ 0.096 567 20¿+. 1 171.¿+ 23.638 0.308 0.207 0.300 516 157.7 122.0 2¿k107 0.138 1.263 0.373 568 111.3 18¿+. 3 22.532 0.027 0.759 0.059 517 291.7 126.7 2¿^.365 0.166 0. 6¿^7 0.236 569 293.¿+ 190.9 23. 1¿+1 0.066 0.28^4 0.0¿+5 518 207.9 127.5 21.¿^76 0.030 1.180 0. 0¿^6 570 313.3 239.3 23.820 0.157 1.528 0.276 519 218.1 132.7 22.578 0. 0¿^2 1.095 0.130 571 25.3 2^2.^ 21.723 0.021 1.620 0. 0¿+7 520 132.¿t 138.1 23.606 0.095 0.313 0.083 572 2¿+0. 1 250.^ 23.293 0.085 -0.076 0.065

TABLE II (Continued) TABLE II (Continued)

Star Χ Y V σΓΤ) ÜTv σ(Β) Star Χ Y V a(V) B-V σ(Β)

573 293.7 261.2 23.215 0.084 -0.165 0.067 625 227.4 206.6 23.274 0.077 -0.393 0.067 57¿f 56.0 293.2 23.^05 0.062 0.277 0.266 626 204.1 264.8 22.653 0.049 0.320 0.064 575 262.0 305.7 23.65¿f 0.092 0.806 0.145 627 278.0 288.8 21.754 0.022 1.070 0.056 576 113.7 338.23.389 0.121 0.440 0.078 628 146.8 403.8 24.040 0.165 0.110 0.136 577 315.^ 368.3 21.95^ 0.030 1.232 0.051 629 310.5 444.8 23.552 0.085 0.536 0.102 578 50.8 378.6 22.023 0.028 1.277 0.036 630 199.3 450.5 22.483 0.041 1.139 Ó.067 579 ^9.8 397.2 23.050 0.036 0.787 0.112 631 253.9 475.0 22.727 0.042 0.968 0.114 580 31.^ ¿+07.7 23.07^ 0.038 0.201 0.057 632 215.0 10.4 23.406 0.072 0.186 0.104 581 293.8 ¿*20.25.708 0.753 -0.721 0.248 633 293.6 45.5 22.555 0.038 0.570 0.047 582 95.0 ¿f2^.0 2^.17^ 0.131 0.490 0.175 634 236.0 136.2 24.510 0.216 0.216 0.185 583 ^3.6 ¿f32.2 23.027 0.052 0.093 0.046 635 189.2 207.9 23.476 0.071 0.695 0.100 58^ 280.9 ¿t80.0 23.12^ 0.083 0.779 0.097 636 220.0 281.3 22.722 0.052 0.109 0.058 585 150.2 ^99.6 23.093 0.081 1.248 0.120 637 61.4 300.1 23.052 0.059 0.702 0.072 586 208.7 2.9 23.275 0.071 0.721 0.109 638 36.5 389.1 22.774 0.043 0.872 0.069 587 275.8 12.7 23.559 0.109 0.722 0.129 £39 263.9 460.6 23.105 0.067 0.971 0.104 588 2^7.0 85.2 23.153 0.066 0.500 0.072 640 198.7 496.8 20.614 0.011 4.498 0.167 589 29^.7 1^.6 23.217 0.088 0.647 0.114 641 294.1 35.1 23.067 0.066 0.589 0.122 590 101.7 192.9 23.1^ 0.056 0.861 0.082 642 258.9 54.5 23.655 0.123 0.483 0.121 591 191.7 198.2 23.783 0.103 0.940 0.195 643 89.9 172.3 23.584 0.083 0.486 0.084 592 107.^ 232.6 23.676 0.077 0.273 0.244 644 196.0 252.8 21.746 .0.036 0.216 0.038 593 290.0 235.9 23.6¿i7 0.154 -0.504 0.067 645 79.6 265.2 24.051 0.150 0.673 0.173 59¿f 225.2 2¿f8.¿f 22.6^1 0.049 -0.054 0.061 646 170.9 273.5 16.619 0.645 -0.760 0.041 595 211.^ 255.3 22.^83 0.046 0.051 0.050 647 317.0 303.0 22.044 0.027 0.084 0.021 596 250.8 270.2 23.^32 0.119 1.014 0.141 648 85.5 360.5 22.535 0.034 0.738 0.096 597 185.^ 275.2 21.8¿t7 0.034 0.936 0.073 649 271.1 438.5 23.451 0.082 0.720 0.126 598 1M.^ 310.^ 23.15^ 0.060 0.056 0.050 650 263.7 439.9 23.508 0.103 0.652 0.095 599 151.5 322.1 20.825 0.010 0.995 0.017 651 165.1 11.3 23.068 0.062 0.180 0.059 600 235.5 337.9 22.970 0.147 -0.005 0.059 652 193.1 54.0 23.615 0.116 0.917 0.131 601 m.9 359.8 22.^09 0.036 0.993 0.050 653 202.6 394.6 23.810 0.123 0.619 0.133 602 16^.7 ^6.1 23.779 0.107 0.817 0.190 654 78.2 419.9 23.599 0.079 0.728 0.115 603 2^+7.9 453.6 22.474 0.027 0.835 0.061 655 305.2 473.0 23.842 0.100 1.492 0.258 604 163.7 457.8 24.489 0.147 -0.042 0.169 656 259.0 60.2 22.685 0.047 0.954 0.069 605 220.7 459.1 23.232 0.105 0.477 0.087 657 282.1 286.5 22.514 0.051 0.815 0.078 606 241.7 464.1 23.255 0.066 0.524 0.103 658 146.5 383.9 23.655 0.338 -0.213 0.073 607 259.2 74.8 24.398 0.250 0.846 0.354 659 313.7 41.0 16.451 1.652 -0.466 0.036 608 222.3 128.1 25.127 0.372 1.150 0.865 660 117.0 275.1 23.686 0.113 0.819 0.124 609 274.8 215.5 22.802 0.057 0.759 0.107 661 45.5 268.4 22.709 0.037 0.884 0.055 610 175.7 235.2 21.610 0.045 0.255 0.044 662 163.0 269.0 20.172 0.044 0.731 0.084 611 268.9 245.2 22.852 0.056 0.715 0.079 663 318.8 483.7 21.531 0.016 1.199 0.038 612 293.8 255.8 22.843 0.065 0.615 0.075 664 294.8 17.3 22.299 0.034 0.872 0.103 613 283.5 296.1 23.947 0.141 -0.493 0.069 665 289.2 143.4 22.675 0.049 0.759 0.065 614 254.9 351.5 23.754 0.106 1.872 0.327 666 309.8 161.8 23.000 0.076 0.677 0.086 615 46.8 358.2 24.807 0.262 0.508 0.322 667 234.0 259.3 22.549 0.055 0.295 0.044 616 160.6 443.5 23.921 0.117 0.446 0.115 668 269.9 103.7 22.137 0.040 1.259 0.085 617 204.1 479.9 23.804 0.097 1.147 0.367 669 209.0 104.2 23.683 0.080 0.283 0.155 618 197.1 76.8 23.177 0.067 0.653 0.108 670 191.6 265.8 20.124 0.024 2.014 0.079 619 293.7 76.7 23.815 0.095 0.116 0.106 671 291.9 319.9 22.501 0.036 0.908 0.069 620 45.9 91.8 22.687 0.038 0.949 0.086 672 54.8 79.4 22.448 0.037 1.030 0.081 621 262.5 192.3 21.561 0.028 1.152 0.035 673 282.8 146.4 23.452 0.060 0.510 0.090 622 238.2 200.2 23.210 0.076 0.022 0.080 674 259.9 360.9 23.195 0.074 0.886 0.103 623 232.1 201.8 22.654 0.041 -0.124 0.048 675 284.7 104.9 22.553 0.066 0.408 0.048 624 226.3 201.6 21.352 0.013 0.870 0.035 676 295.5 451.2 23.681 0.134 0.396 0.138

TABLE II (Continued) TABLE III

Internal Photometric Errors and Completeness Star Χ Y V σ( V ) B-V σ(Β)

Magnitude Random Error σ Complet. Fraction f 677 232.0 193.9 21.909 0.027 0.773 0.052 678 226.7 16^.9 19.3^9 0.020 1.134 0.038 679 316.3 200.8 21.6M 0.022 1.209 0.036 V=18.0 0.008 1.00 680 203.8 2^6.1 19.231 0.009 0.786 0.042 19.0 0.011 0.99 681 229.237.3 21.3^ 0.022 0.376 0.040 20.0 0.020 0.97 682 159.8 236.6 21.970 0.034 0.617 0.076 20.5 " 0.030 0.96 683 232.232.6 20.380 0.009 1.615 0.044 21.0 0.042 0.94 68¿+ 285.^ ^62.6 21.758 0.047 1.374 0.074 21.5 0.062 0.91 685 282!0 463.21 .068 0.026 1.189 0.035 22.0 0.088 0.87 0.232 0.677 0.195 22.5 0.125 0.78 686 311.2 34.4 20.886 23.0 0.171 0.66 687 300.0 38.6 21.619 0.028 0.878 0.046 23.5 0.230 0.50 688 268.2 485.1 19.433 0.022 1.787 0.041 689 266.2 488.4 21.549 0.061 0.921 0.051 B=19 * 0 0.008 1.00 690 307.6 39.3 20.884 0.252 0.393 0.181 20.0 0.011 1.00 691 195.1 349.0 21.545 1.969 0.921 0.159 21.0 0.018 1.00 21.5 0.025 0.99 22.0 0.033 0.98 enth columns give the internal standard errors in V and Β 22.5 0.045 0.96 generated from the ALLSTAR code. 23.0 0.065 0.91 23.5 0.094 0.79 To estimate the internal accuracy and detection com- 24.0 0.139 0.62 pleteness of our photometry as a function of magnitude, 24.5 0.250 0.36 we used the ADDSTAR facility in DAOPHOT. We adopted the recommended procedure (Stetson 1987) tak- ing the original CCD frame, adding a random sample of artificial stars (i.e., scaled PSFs) to it, and then remeasur- ing the entire frame through FIND and ALLSTAR in just the same way as the real data. The fraction of artificial stars recovered gives the completeness of detection, and the mean quadratic magnitude difference (their input magnitude minus their recovered value) gives the internal uncertainty of the photometry. We then binned the artificial stars in intervals of V magnitudes and drew smooth curves through the average data for each bin. The same procedure was repeated for the Β frame. The results of these tests are given in Table III and illustrated in Figure 2. It is clear that for V > 22 and Β > Fig. 2-Internal uncertainty σ and completeness fraction f of the photometry plotted as a function of magnitude. In each case the left-hand 23 incompleteness corrections become significant and the ordinate refers to σν, σΒ and the right-hand scale tofv,fB. photometric errors rise rapidly.

IV. Color-Magnitude Diagram and diagram appearance depends on the location within the Luminosity Function frame. Figure 4(a) displays the C-M diagram obtained The observational data about the Phoenix galaxy consist from a circle (zone A) centered on frame coordinates {x = of the color-magnitude (C-M) diagram and of the luminos- 190, y = 260) and with a radius of r = 100 pixels (~ 36 arc ity function we may extract from the data of Table II. sec), while Figure 4(b) displays the C-M diagram ob- Some additional information (which will be used in the tained from the regions of the frame (zone B) farther than following discussion) may be inferred from the (low-qual- 120 pixels (~ 44 arc sec) from the same position. Zone A ity) U and Ha frames of the same western region of the approximately corresponds to the region of the galaxy galaxy we are considering here. We note that the basic occupied by the association described by Canterna and issue is the determination of a distance modulus (at least Flower (which is very prominent in our U frame). In the crude) for the Phoenix galaxy. following we will call zone A "association" and zone Β The C-M diagram is displayed in Figure 3. The C-M "field". The C-M diagrams of the two panels of Figure 4

PHOENIX PHOENIX All Stars AsaoolaHon

V ' + ++aIÎ^++ + -τ . ++vV: ++î+ + + + . \-v + + ^fwîflf+ + + + + >4 + + /^ + + + + + +++ + í+ ++ + v V í f + * y + + 1 * ta

ι γ- -I 1 0.80 0.0 0.8 1.6 9-v B-V Fig. 3-The C-M diagram for the Phoenix galaxy from the DAOPHOT PHOENIX photometry. Held of th· galaxy look rather different: in the association region, the population of bright blue stars is quite the same as that of bright red stars, while in the field region there is a large population of bright red stars and a few blue ones. This subdivi- + sion is clearly reminiscent of the classical subdivision + between Population I and Population II stars (Baade + ++++ ί-^+ + + 1944). A luminosity function has been constructed for the observed field in the Phoenix dwarf galaxy. It is listed in Table IV: the first column lists the V magnitude range adopted for each bin; the second column gives the mean 0.80 B-V magnitude (V) for the sample of stars found therein. The third column gives the incompleteness factor for that bin. Fig. 4-(a) The C-M diagram for the region within a radius of 100 pixels (= 36") from the position of coordinate χ = 190, y = 260 ("association"); The fourth column lists the number of stars observed in and (b) the C-M diagram for the region further than 120 pixels (= 44") each bin, and the fifth column lists the estimated number from the same position ("field"). of stars after correction for incompleteness. In order to obtain a meaningful galaxy-luminosity function the field- star contribution (due to our Galaxy) must be subtracted TABLE IV from the data, although this is not a critical correction Luminosity Function here due to the high galactic latitude of the Phoenix dwarf galaxy. Since it is impossible to discriminate between Number of Stars field and galaxy stars on the basis of their location on the V mag. range '/. Compl. Total Corr . Field Galaxy C-M diagram, we have chosen to sum all stars regardless of observed color within each V magnitude bin and then 19.50-20.00 19.8^ 0.98 2 2.0 0.6 1.4 20.00-20.50 20.22 0.96 9 9.4 0.7 8.7 to subtract the field-star contribution of stars within the 20.50-21.00 20.80 0.94 2A 25.5 0.8 24.7 same V magnitude range. Model galactic star counts 21.00-21.50 21 .26 0.92 38 41.3 0.8 40.5 21.50-22.00 21 .76 0.89 74 83. 1 0.9 82.2 based on Bahcall and Soneira (1980) were used. The 22.00-22.50 22.27 0.82 88 107.3 1 .0 106.3 field-star contribution to each magnitude interval is listed 22.50-23.00 22.73 0.72 115 159.7 1 .0 158.7 in the sixth column of Table IV, and the final galaxy 23.00-23.50 23.25 0.60 143 238.3 1.2 237.1 23.50-24.00 23.73 0.40 129 322.5 1.3 321.2 luminosity function is listed in the seventh column. V. Phoenix Galaxy Field Population Red stars apparently describe a sequence in the C-M bility of detection (as given by the experiments with diagram. This effect is not due to observational selection, artificial stars) falls to 0.5. For colors redder than (ß —V) as is shown by Figure 5, where the same C-M diagram of = 1.2, the excess of observed stars brighter than V = 22 is Figure 4(b) is given, with a line drawn where the proba- clearly large with respect to the measured stars with 22 <

PHOENIX A. Comparison with Dwarf Irregular Galaxies Field of the galaxy The C-M diagram of the Phoenix galaxy, dominated by red stars, appears dramatically different from the C-M diagram of typical irregular galaxies, where most of the brighter stars are rather blue. Observationally, in a typical irregular galaxy, the ratio r of blue (here, (Β —V) < 0.7) to red stars (here, (ß —V) > 0.7) is quite independent of the magnitude for the two or three brightest magnitudes {Mv < —4), the blue stars outnumbering the red ones by a factor of two or more. Table V lists the ratios r obtained from data in the literature for some typical dwarf irregular galaxies, within about three magnitudes of the brightest star, and for the Phoenix dwarf galaxy (both from the entire observed frame and from the field region only). Data are given (with B-V their references, second column) for those dwarf irregular Fig. 5-The C-M diagram for the field region of the Phoenix galaxy. galaxies (other than the Magellanic Clouds) for which Superimposed is a line representing the magnitudes and colors at which quite extensive photometry of resolved stars exists (more the probability of detection (estimated from artificial star experiments) is 0.5. than 100 stars), above a reasonable limit of completeness (which is given in the third column). These limits were V < 23 (for which the probability of detection is still quite estimated by the appearance of the C-M diagram and may high). be somewhat erroneous. The very extensive literature There are three possible interpretations for the red data concerning NGC 6822 were not considered here, sequence in the Phoenix galaxy field C-M diagram: since galactic contamination is very strong for this galaxy. 1. It is composed of red supergiants with V magnitudes The galaxies of Table V all lie at high galactic latitude and up to Mv 7. In this case the distance modulus of the have little foreground reddening (fifth column), as given Phoenix galaxy is (m — M ~ 27. If this interpretation is by the references in the sixth column. The number of blue correct, the Phoenix galaxy would resemble dwarf irregu- ((B — V) < 0.7) and red ((Β —V) > 0.7) stars are given in lar galaxies (following the interpretation given by the seventh and eighth columns, respectively. These Canterna and Flower). numbers were not corrected for field contamination 2. It is composed of bright asymptotic-giant-branch which is, however, quite small given the high galactic (AGB) stars. The brightest magnitude of AGB stars de- latitude of these galaxies. For Holmberg I and II, we pends on the age of the system (see, e.g., Iben and transformed the original GR colors into BV ones by using Renzini 1983), though this uncertainty is not too critical in the color transformations given by Hoessel and Mould 8 the present discussion. If the age is of the order of 10 yr, (1982). The ratios r are given in the ninth column. The then the AGB is predicted to be extended up to ~ —5. uncertainties in r were obtained by the formula (see Iben It would be slightly brighter for smaller ages and slightly 1971) fainter for larger ones. The distance modulus would then (N -1/2 + N -1/2)N /N . be (m — M)v ~ 25.5 and the galaxy would be of an B R B fí intermediate class between irregular and spheroidal, 8 As anticipated above, the blue bright stars outnumber dominated by a stellar population having an age ~ 10 yr the red ones by roughly a factor of 2 in dwarf irregular (similar to that of the populous cluster NGC 1866 in the galaxies. The larger value obtained for Sextans A might be LMC; see, e.g.. Flower (1977), but being at present in a due to a star-formation rate presently larger than in the rather quiescent state with a small amount of star forma- past (Aparicio et al. 1987). The value of r for the Phoenix tion (like the Pegasus dwarf galaxy: Hoessel and Mould galaxy field is r = 0.56 ± 0.08 and increases to only r = 1982). 0.70 ± 0.08 when all the observed field (including the 3. It is composed of red-giant-branch (RGB) stars with association) is considered. This would indicate that more V magnitudes up to Mv 3. Within this scheme, the stars are observed in the red-supergiant phase than in distance modulus would he {m — M)v ~ 23, and the galaxy earlier phases of evolution, which is unlikely. We there- would belong to the Local Group. It would resemble a fore reject the hypothesis that the brighter red stars in the dwarf spheroidal, dominated by an old population {t> 0.3 Phoenix dwarf galaxy are supergiants. Gyr). The association population would in this case be due to a burst of star formation ~ 108 yrs ago. Β. The Intermediate-Age Hypothesis We will now consider these three hypotheses in more Theoretical models (Becker and Iben 1979, 1980; Ren- detail. zini and Voli 1981) predict the extension of the AGB up to

TABLE V Ratio of Blue (B-V<0.7) to Red {B-V>0.7) Stars in Dwarf Irregular Galaxies

Galaxy Ref. v., (m-M) E(B-V) Ref.

IC 1613 1 20.0 2^.5 0.03 1 90 1.8810.^7 Sextans A 2 22.0 25.6 0.02 ^ 665 228 2.92+0.31 Holmberg I 3 23.0 27.5 0.03 3 125 78 1.60+0.32 Holmberg II 3 22.0 27.5 0.02 3 265 130 2.0^++0.30 Phoeni χ All 2^.0 0.02 259 363 0.71+0.08 Field 2^.0 0.02 IM 250 0.56±0.08

References : 1. Sandage and Katem, 1976; 2. Aparicio et al., 1987; 3. Hoessel and Danielson, 198^; Sandage and Carlson, 1982.

luminosities ~ —7, the exact value depending the Phoenix dwarf galaxy is due to the AGB of intermedi- slightly on the age. This bolometric magnitude corre- ate-mass stars. In any case, we note that a similar inter- sponds to Mv ~ —5 (Becker and Mathews 1983). How- pretation would produce an estimate of (m — M )„ ~ 24 for ever, the observed (Richer 1981; Cohen et al. 1981) lumi- the distance modulus of the Phoenix dwarf galaxy, which nosity function for C stars in the Magellanic Clouds is not much larger than the value we will infer from the suggests that the upper-luminosity limit of the AGE is comparison with the RGB of old populations in the next actually considerably fainter (probably due to heavy mass section. loss by stars ascending the AGB: see, e.g., Iben and Renzini (1983). The brightest stars in the young populous C. The Phoenix Galaxy as a Dwarf Spheroidal cluster NGC 1866 in the LMC (Flower 1981), with an If the field of the Phoenix galaxy is dominated by an old age of f ~ 108 yrs or slightly younger, have an absolute or intermediate-age population (like that of galactic glob- magnitude of ~ —3.5. The giant branch of NGC 1866 ular clusters, or in the field of the Magellanic Clouds), the is quite poorly defined; there are, on the other hand, location of the RGB may be used as a distance indicator for several Cepheids at intermediate colors ((ß —V) ~ 0.6), the galaxy. and absolute magnitudes close to Mv~ —3, correspond- Figure 6(a) compares the C-M diagram for the field ing to the blue loop in the core-helium-burning phase (see region of the Phoenix dwarf galaxy with the mean loci for Becker and Mathews 1983). Though there may be some three galactic globular clusters: 47 Tucanae (Hesser et al. population effect, the general appearance of the C-M 1987), M 3, and M 92 (Sandage 1970). The cluster mean diagram of the Phoenix field is quite different from that of loci were adjusted for reddening and arbitrarily shifted NGC 1866. vertically to account for the distance modulus difference The small number of extremely red stars (see Section between the galaxy and the clusters. Reddenings and VII) also suggests that very few bright AGB stars are distance moduli for the globular clusters were taken from present in the Phoenix dwarf galaxy. We find only two Gratton (1985). The distance moduli are somewhat uncer- candidate C stars (i.e., stars redder than (B—V) = 2) tain (±0.2 mag); however, this uncertainty is irrelevant over a total of622 stars brighter than V = 24 in the portion here. Using data listed by Gratton (1985), we have values of the Galaxy surveyed by the present photometry. As of 13.2, 15.0, and 14.6 for 47 Tue, M 3, and M 92, respec- a comparison, photometry of 388 stars in the Pegasus tively (averaging results obtained through ZAHB and dwarf galaxy (Hoessel and Mould 1982) produced 22 ob- PLA methods). jects redder than {B — V)= 2. Still higher proportions of Figure 6(b) compares the same C-M diagram of the extremely red stars are obtained from photometry of field of the Phoenix galaxy with the location of the giant other dwarf irregular galaxies (see, e.g., the references in branches of fields in the Magellanic Clouds (Hardy et al. Table V). 1984; Hardy and Durand 1984). Analogous vertical shifts We would therefore consider as improbable that the were allowed here, too. The distance moduli of the Ma- dominant contribution to the red sequence of the field of gellanic Clouds have been the subject of a considerable

PHOENIX red stars ((ß — V) > 0.4) in the field of the Phoenix galaxy Field of the galaxy (corrected for incompleteness and field-star contribution) with the luminosity function of M 3 (Sandage 1957), M 92 (Hartwick 1970), and 47 Tue (Hesser et al. 1987). Only the giant branches were considered for M 92 and M 3, for which the horizontal branches are mostly bluer than (B — V)= 0.4. Figure 7(b) displays analogous comparisons with the luminosity functions for the red stars of the field of the LMC (Hardy et al. 1984) and of the SMC (Hardy and Durand 1984). The same differences between the distance moduli used in Figure 6 were adopted here. The overall comparison between the C-M diagram of the field of the Phoenix dwarf galaxy and those of old or intermediate-age stellar populations (Fig. 6) shows a good agreement, and it is compatible with the hypothesis that the observed red sequence of Figure 5 is the RGB of an B-V old population {t> 0.3 Gyr). Table VI collects the various Ρ HOE NIX estimates of the distance modulus that may be obtained Field of the galaxy by these procedures. They range from (m —M) = 21.8 given by the comparison with 47 Tue to {m — M)v = 23.6 18- SMC given by the comparison with M 92. The value to be L MC preferred depends on the age and metallicity of the popu- 19- lation of the Phoenix galaxy. 20- If the observed red-giant branch of the Phoenix galaxy belongs to an old population, we expect a horizontal > 21- branch (or a clump) to be present at an absolute magni- 22- tude within the interval 0.5 < < 1. This would correspond to the core-helium-burning phase. It would appear 23- brighter than the limiting magnitude of our photometry if 24- the RGB of the Phoenix galaxy is matched with those of rather metal-rich populations (like 47 Tue or the fields of 25- -Γ- the Magellanic Clouds). In these cases, we would expect a -0.4 Ι.6 B-V bump in the luminosity function at a magnitude of V ~ Fig. 6-(a) Comparison of the C-M diagram for the field region of the 22.8. No similar bump is observed (see Fig. 7). Further- Phoenix galaxy with the mean loci for the globular clusters 47 Tue more, if the population of the field of the Phoenix dwarf (Hesser et al. 1987: solid line), M 3 (Sandage 1970: dashed line), and galaxy is as young as that of the Magellanic Clouds, there M 92 (Sandage 1970: dash and dotted line); and (b) with the mean loci for the SMC (Hardy and Durand 1984: solid line) and the LMC (Hardy et al. 1984: dashed line). Appropriate horizontal shifts for differences in red- TABLE VI dening (see text) were applied. The mean loci of the comparison objects have been adjusted to fit the red-giant branch of the field of the Phoenix Distance Modulus Estimates for the Phoenix Galaxy galaxy. Compar ison (m-t^Dv (m-MK (m-M)ν debate in the last few years. The adopted values were □b ject (Object ) (Phoeni χ ) from Reid and Strugnell (1986) for the LMC ((m — M)v = 18.4, E{B —V) = 0.06), and from Caldwell and Coulson (1985: E{B—V) = 0.05) and Seidel, Da Costa, and De- Globular Clusters; marque (1987: {m — M)v = 18.95) for the SMC. These choices correspond to the adoption of the so-called short Tue 13.2 8.6 21 .8 M3 15.0 8.0 23.0 distance scale (see Rich, Da Costa, and Mould 1984). M92 1^.6 9.0 23.6 Finally, a reddening of E{B—V) = 0.02 ± 0.02 was adopted for the Phoenix galaxy in both panels of Figure 6, Magellanic Clouds: in agreement with the maps by Burstein and Heiles (1982) LMC 18.^ 3.6 22.0 and with cosecant law estimates (Reed, Hesser, and SMC 19.0 3.5 22.5 Shawl 1988). Figure 7(a) compares the luminosity function for the

© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System PHOENIX DWARF GALAXY 1419 would be a lack of red stars fainter than V = 23.5 (due to modulus is thus (m — Μ)υ = 23.5 ± 0.5, which corre- the small number of expected subgiants). Stars fainter sponds to a distance of 500 ± 130 kpc, placing the than this limit are close to the limit of our photometry; Phoenix galaxy well within the limits of the Local Group. however, a large number of red stars fainter than V = 23.5 This estimate of the distance modulus is far smaller than is observed. In the cases of the comparisons with metal- the value of (m — M )^ = 26.3 ±0.2 obtained by Can terna poor populations (like those of the globular clusters M 3 and Flower under the assumption that the brightest red and M 92), the bump in the luminosity function due to the stars are supergiants. presence of the horizontal branch is expected to be below The question may be raised whether the observed or just at the limits of our observations (and part of the HB width of the giant branch of the Phoenix dwarf galaxy is might be bluer than (Β -V) = 0.4). Figure 7(a) shows that due to a spread in metal abundance. To address this, there is a good match between the present luminosity fiducial mean loci for the giant branch (stars with {Β —V) function and those of these metal-poor old populations. > 0.4) of the field of the Phoenix dwarf galaxy were However, we note that the RGB and the magnitude of the derived by an iterative procedure, by rejecting those stars horizontal branches are insensitive to even quite large with {Β —V) values lying more than 2 times the standard changes in the age of a population, insofar as this is older deviation σ from the average calculated for intervals of V than a couple of Gyr. Therefore, a better guess on the age magnitude from the data of Table II. These mean loci, and of the population of the field of the Phoenix galaxy might final values of the a s obtained by this procedure, are be derived either by a luminosity function reaching as far listed in Table VII. Stars included in the σ calculation as V = 25.5 or by observations of RR Lyrae stars (which have distributions in (β — V) somewhat broader than esti- would be at V ~ 24). mated from artificial star experiments for V < 22.5 (where Once the similarity to the old metal-poor clusters is errors are reasonably small and blue stars are irrelevant). accepted, the best guess for the Phoenix galaxy distance The derived intrinsic width of the giant branch is ~ 0.14

3 3

2 2

1 1

20 22 24 26 20 22 24 26

Fig. 7-(a) Comparison of the cumulative luminosity function for the red stars ((Β — V) > 0.4) in the field region of the Phoenix dwarf galaxy, with analogous cumulative luminosity functions for the globular clusters 47 Tue (Hesser et al. 1987: solid line), M 3 (Sandage 1957: dashed line), and M 92 (Hartwick 1970: dash and dotted line); and (b) with the cumulative luminosity functions for red stars for the SMC (Hardy and Durand 1984: dashed line) and the LMC (Hardy et al. 1984: solid line). The same distance modulus differences used in Figure 6 are adopted here. Luminosity functions were normalized to produce the same number of stars brighter than the faintest magnitude available.

centered on the point of coordinates χ = 190, y = 260 TABLE VII (including 174 stars); and we selected as a comparison Red Giant Mean Loci field a region of equivalent area, composed of two equal rectangles at the upper and lower edges of the frame (these were selected because they are farthest from the V mag. range σ( Β -V) association), including 100 stars. We then ordered the stars in V magnitude both in the association and in the 20.50-21.00 20.82 1.292 0.167 comparison fields, and stepped star by star in the com- 21.00-21.50 21.25 1.25^ 0.092 parison field looking for the closest neighborhood in a 21.50-22.00 21 .73 1.1^7 0. 114 distorted C-M diagram (where V magnitude was multi- 22.00-22.50 22.27 0.933 0.176 22.50-23.00 22.76 0.834 0. 144 plied by 0.2). When the closest neighborhood in the 23.00-23.50 23.23 0.740 0.198 association region was closer to the position in this dis- 23.50-2^.00 23.72 0.655 0. 141 torted C-M diagram of the star of the comparison field than a critical radius p, both stars were eliminated from the respective lists. We tested several values of ρ and found that very few more stars are deleted if ρ > 0.20. We mag (2 σ), corresponding to a spread in metal abundance therefore adopted this value of ρ = 0.20 as the critical of about 0.6 dex. As a visual comparison, Figure 8 displays radius in this subtraction technique. For this value of p, the mean loci for the same three globular clusters consid- 19 stars of the comparison fields (mostly at faint magni- ered above (47 Tue, M 3, and M 92), and the C-M dia- tudes) still were unmatched. This figure is quite high to gram of the field of the Phoenix galaxy, under the assump- be due only to chance. We think rather that more faint tion that the distance modulus is (m — M),, = 23.0 (as stars are undetected in the association region (which is a given by the match with the M 3 giant branch). The little more crowded) than in the comparison regions. amplitude of the observed spread of the giant branch of However, we do not think that this consideration affects the Phoenix dwarf galaxy is similar to that observed in the the following discussion. Fornax dwarf spheroidal (Buonanno et al. 1985). The C-M diagram of the association in Phoenix obtained by this subtraction technique is displayed in Fig- VI. Association ure 9. A sequence of blue stars is present in this C-M The C-M diagram for the "association" region in Figure diagram, which may be interpreted as the main sequence 8 4(a) is heavily contaminated by stars which belong to the of a population having an age of about 10 yr (if the general field of the Phoenix galaxy. We therefore decided distance modulus of (m — M ) = 23.5 ± 0.5 derived from to perform a subtraction of field stars before attempting a the Phoenix field (C-M) diagram is adopted). The turn-off discussion of the association. We selected as the associa- point of this C-M diagram is not very well defined, per- tion region the circular area of radius R = 100 pixels, haps due to a spread in age. Several stars redder than {Β—V) = 0.7 indicate the presence of evolved stars. A PHOENIX comparison with the C-M diagram of the populous cluster Field of the galaxy PHOENIX Association (field subtracted)

18- 19- 20- > 21- ++ + 22- + + + % + + + + + + * + +++ + ^ + + V+ i+, +

I 1 r- Fig. 8-Comparison of the C-M diagram for the field region of the 0.0 0.4 0.8 Phoenix galaxy, with the mean loci for the globular clusters 47 Tue B-V (Hesser et al. 1987; solid line), M 3 (Sandage 1970: dashed line), and M 92 (Sandage 1970: dash and dotted line). A distance modulus of Fig. 9-The C-M diagram for the association region in the Phoenix {m ^ M)v = 23.0 was adopted for the Phoenix galaxy. galaxy, after removal of field stars (see text).

NGC 1866 in the LMC (Flower 1981) indicates that the estimated by star counts on reproductions of the Can terna giant branch of the association in the Phoenix galaxy (at a and Flower plates). The radio observations by Morras and color of(B-V)o~ 0.9) is bluer than that of NGC 1866 (at Bajaja (1986) produced upper limits of ~ 106 SJÎ© for the

{B — V)0 ~ 1.2). This might be an indication of a consider- total mass of Η ι within the optical image of the galaxy, if a ably lower metal content ([Fe/H] ~ —2 for the Phoenix distance of 500 kpc is used, rather than the value of 1.85 galaxy association), which would be in agreement with the Mpc given by Canterna and Flower. However, the total faint integrated magnitude of the galaxy. It also would mass of H I in the filament projected in the direction of 8 favor a distance modulus larger than (m — M)v = 23. the Phoenix galaxy might be as high as ~ 10 ÏR© (again, Three stars (Nos. 140, 315, and 337) at (Β —V) ~ 0.75 and for a distance of500 kpc). V ~ 20.4 lie approximately where stars on the blue loop in We finally note that the Phoenix dwarf galaxy appears the core-helium-burning phase of intermediate mass stars similar to the dwarf galaxy in Pegasus (Hoessel and Mould are expected. Therefore, these stars may be considered as 1982): in both galaxies a recent burst of star formation candidates to be Cepheids. Adequate observations of created a small amount of young population in a dwarf these stars would clearly be very interesting. galaxy dominated by an old population. They seem to belong to an intermediate class between typical irregular VIL Red Stars galaxies (which are presently undergoing star formation) An inspection of the data of Table II reveals only a small and dwarf spheroidals, where star formation halted a long number of very red stars {Β —V) > 1.8). Only two of them time ago (some 109 yrs ago). However, even for dwarf are brighter than V ~ 22 (Nos. 640 and 670). Our photom- spheroidals, several bursts of star formation likely oc- etry produces an extremely red color for the clean, un- curred. For instance, in the case of the Fornax dwarf blended star 640 (ß —V) = 4.45), close to the upper edge spheroidal, evidences for a relatively young population of the frame. The color is clearly unreliable being far out were found by several authors (Demers and Kunkel 1980; of the calibration limit. However, a direct inspection of Aaronson and Mould 1980; Frogel et al. 1982; Richer and the Β and V frames (which were taken consecutively on Westerlund 1983; Buonanno et al. 1985; Gratton and the same night) confirms the extremely red color of the Ortolani 1987). How these galaxies were able to preserve star, which is also prominent in Ha. Star 670 is very close their gas, and to have more bursts of star formation, is still to the adopted center for the association. Both objects unknown. The cases of the Pegasus and Phoenix dwarf might be C stars. galaxies (which have undergone star formation quite re- cently and are far from other galaxies) might be important VIIL The Nature of the Phoenix Dwarf Galaxy in this respect. It is interesting that the Phoenix galaxy is The Phoenix dwarf galaxy appears to be a small galaxy not far from the Magellanic Stream and might be within a larger H I cloud. More investigations on this object are {Mv 11), dominated by an old population, with a small amount of young stars. The total mass of the young popu- clearly welcomed. lation is very uncertain. Flowers (1981) photometry for We wish to thank Dr. O.-G. Richter for several inter- NGC 1866 produced about 80 red giants {B—V) > 0.4), esting discussions and for having given us material in while only about 20 are present in the Phoenix associa- advance of publication, Dr. P. Stetson for his advice tion. 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